Highlight cells in heatmap

I created a heatmap where each cell represents a temperature value using the commands:

cdata = [values of temperature]

xvalues = [0,1,2,3,etc.]

yvalues = [0,1,2,3,etc.]

h = heatmap(xvalues,yvalues,cdata)

I need to:

• command to highlight cells over a limit (for example 500)
• Highlight cells within a given range (for example 300 to 800)

It is not important how the cells are highlighted, it can be a different colour (like green or blue), or a cross X on top of the cells.

Thanks for the help

Answer 1

[Rishik Ramena]

You can do so by creating a custom colormap. The code below shows a simple implementation.

xvalues = 1:5;
yvalues = 1:5;
cdata = randi(20,[5,5]); % range of values in cells < 20
cmap = [repmat([1 0 0],5,1)
    repmat([1 1 1],5,1) % highlight all cells with values from 5-10 with white
    repmat([0 0 0],10,1)]; % highlight all cells > 10 with black

heatmap(1:5,1:5,randi(20,[5 5]),'Colormap',cmap);

[Ilyass Boukhari]

Hey Rishik thanks for your help!

I tried replace your example values with my array size and values, so that it would fit my actual needs

xvalues = 1:25 ; 
yvalues = 1:25
 
cdata = 
   100   100   100   100   100   100   100   100   100
   300   300   300   300   250   200   180   150   100
   500   500   500   300   250   200   180   150   100
   550   500   450   300   250   200   180   150   100
   600   600   500   400   300   200   180   150   100
   740   700   600   500   300   200   180   150   100
   700   600   500   450   400   200   180   150   100
   600   500   400   300   250   200   180   150   100
   500   450   450   300   300   250   200   150   100
   500   450   450   550   450   250   230   200   100
   450   450   550   700   700   250   230   200   100
   400   300   500   650   650   250   200   150   100
   400   300   400   450   300   250   200   150   100
   350   380   380   380   300   250   200   150   100
   380   350   380   380   300   250   200   150   100
   650   500   350   390   300   300   200   150   100
   700   400   370   350   300   300   200   150   100
   500   400   360   350   300   300   200   150   100
   300   300   350   350   300     0   200   150   100
   200   200   200   200   200   100   100   100   100
   100   100   100   100   100   100   100   100   100
   100   100   100   100   100   100   100   100   100
   100   100   100   100   100   100   100   100   100
   250   250   250   250     0     0     0     0   100
   100   100   100   100   100   100   100   100   100 
 
cmap = [repmat([0 0 0],200,1 ) %black background
    repmat([1 1 1],200,1) % highlight all cells with values from 200-750 white 
    repmat([1 0 0],750,1)]; % highlight all cells > 750 with red (highest)
 
heatmap(1:25,1:25,cdata,'Colormap',cmap);

however this is the result (as you can see the map doesn't reflect the aimed ranges)

What am I doing wrong?

Your help is much appreciated

[Rishik Ramena]

The second argument for repmat denotes the number of rows to be repeated for the RGB vector given in its first argument. So the cmap contains rows of RGB values which are equal in number to the range of values in the cdata (max-min). For visualisation, try imagining filling the colors on the colorbar from the bottom while creating a custom colormap.

max_val = max(cdata(:)) % get the max value from cdata
cmap = [repmat([1 0 0],200,1) % first 200 rows (0-199)
repmat([1 1 1],750-200,1) % 200-749
repmat([0 0 0],max_val-750,1)]; % >= 750

[Ilyass Boukhari]

All clear! Thank you for your help!